1. Field of the Invention
The present invention relates to a method of achieving a biologic effect in a mammal comprising the incorporation of calcitonin into liposomes, and parenterally administering the liposome-entrapped calcitonin preparation into the body of said mammal.
2. Description of the Prior Art
Calcitonin is a polypeptide hormone secreted by the parafollicular cells of the thyroid gland in mammals and by the ultimobranchial gland of birds and fish.
Calcitonin-salmon is of salmon origin or synthetic origin, both having 32 amino acids arranged in the same linear sequence. Salmon calcitonin appears to have actions essentially identical to calcitonins of mammalian origin, but with greater potency and longer duration of action. It is presently accepted that endogenous calcitonin participates with parathyroid hormones in the homeostatic regulation of blood calcium.
Calcitonin is used in the treatment of various diseases related to abnormal skeletal metabolism (e.g. hypercalcemia, Paget's disease). Chronic therapy, however, requires daily adminisitration by parenteral injection. For that reason, it has been desired to develop new formulations so as to extend the duration of the presence of calcitonin in the tissue affected by the disease or to retain a high effective level for a long period of time by a small dose administration by intramuscular or intravenous route, thereby decreasing the frequency of administration. In addition, it has also been desired to obtain specificity with calcitonin so that it reaches its target selectively and in a controlled fashion, thereby reducing the incidence of side effects.
Liposomes have been noted as carriers for drugs, enzymes, hormones, heavy metal detoxification therapy and cancer chemotherapy in order to increase affinity of the active agents with target cells and tissues, and to alleviate their side effects. Studies have indicated that liposomes, upon parenteral injection into mammals, are taken up rapidly by cells and intracellular lysosomes of the reticuloendothelial system. Due to their relative impermeability, substances incorporated in liposomes remain concentrated and are unexposed to plasma. These characteristics suggest their suitability as carriers for calcitonin.
Liposomes are composed of phospholipids. Phospholipids have the dual characterisics of being both hydrophilic and hydrophobic at the same time. Under certain conditions phospholipids will assemble to form a double layer or bilayer. In the presence of water the bilayers form into closed spherical shapes producing the basic or simplest liposome entities. Further bilayers can be added to the basic single bilayer liposome forming concentric, closed spherical structures that range from 25 nanometers to several micrometers in diameter. The central region of the multi-layered liposome and areas between the bilayers contain water, but water is excluded from the interior, hydrophobic region of the bilayer itself. An active substance can be incorporated either into the aqueous or non-aqueous regions.
Generally, two techniques are used for incorporation of an active substance in lipsome. One technique involves dissolving the appropriate lipids in an organic solvent, which is subsequently removed, leaving behind a thin film. The substance to be incorporated is added to the film in water; the film dispersed on shaking forms individual liposomes with the entrapped substance. The other technique involves the use of lipid-soluble active substances which are dissolved together with the lipids.